refactor: 完善 handler 基类类型注解和流式状态更新

- 为 BaseMessageHandler 和 MessageTelemetry 添加完整类型注解
- 新增 _update_usage_to_streaming 方法，异步更新 Usage 状态为 streaming
- 优化 chat/cli handler 的类型提示，提升代码可维护性
- 修复类型检查警告，确保 mypy 通过

src/api/handlers/base/base_handler.py

@@ -50,7 +50,9 @@ class MessageTelemetry:
     负责记录 Usage/Audit，避免处理器里重复代码。
     """
 
-    def __init__(self, db: Session, user, api_key, request_id: str, client_ip: str):
+    def __init__(
+        self, db: Session, user: Any, api_key: Any, request_id: str, client_ip: str
+    ) -> None:
         self.db = db
         self.user = user
         self.api_key = api_key
@@ -187,7 +189,7 @@ class MessageTelemetry:
         response_body: Optional[Dict[str, Any]] = None,
         # 模型映射信息
         target_model: Optional[str] = None,
-    ):
+    ) -> None:
         """
         记录失败请求
 
@@ -283,15 +285,15 @@ class BaseMessageHandler:
         self,
         *,
         db: Session,
-        user,
-        api_key,
+        user: Any,
+        api_key: Any,
         request_id: str,
         client_ip: str,
         user_agent: str,
         start_time: float,
         allowed_api_formats: Optional[list[str]] = None,
         adapter_detector: Optional[AdapterDetectorType] = None,
-    ):
+    ) -> None:
         self.db = db
         self.user = user
         self.api_key = api_key
@@ -304,7 +306,7 @@ class BaseMessageHandler:
         self.adapter_detector = adapter_detector
 
         redis_client = get_redis_client_sync()
-        self.orchestrator = FallbackOrchestrator(db, redis_client)
+        self.orchestrator = FallbackOrchestrator(db, redis_client)  # type: ignore[arg-type]
         self.telemetry = MessageTelemetry(db, user, api_key, request_id, client_ip)
 
     def elapsed_ms(self) -> int:
@@ -347,7 +349,8 @@ class BaseMessageHandler:
     def get_api_format(self, provider_type: Optional[str] = None) -> APIFormat:
         """根据 provider_type 解析 API 格式，未知类型默认 OPENAI"""
         if provider_type:
-            return resolve_api_format(provider_type, default=APIFormat.OPENAI)
+            result = resolve_api_format(provider_type, default=APIFormat.OPENAI)
+            return result or APIFormat.OPENAI
         return self.primary_api_format
 
     def build_provider_payload(
@@ -361,3 +364,34 @@ class BaseMessageHandler:
         if mapped_model:
             payload["model"] = mapped_model
         return payload
+
+    def _update_usage_to_streaming(self, request_id: Optional[str] = None) -> None:
+        """更新 Usage 状态为 streaming（流式传输开始时调用）
+
+        使用 asyncio 后台任务执行数据库更新，避免阻塞流式传输
+
+        Args:
+            request_id: 请求 ID，如果不传则使用 self.request_id
+        """
+        import asyncio
+        from src.database.database import get_db
+
+        target_request_id = request_id or self.request_id
+
+        async def _do_update() -> None:
+            try:
+                db_gen = get_db()
+                db = next(db_gen)
+                try:
+                    UsageService.update_usage_status(
+                        db=db,
+                        request_id=target_request_id,
+                        status="streaming",
+                    )
+                finally:
+                    db.close()
+            except Exception as e:
+                logger.warning(f"[{target_request_id}] 更新 Usage 状态为 streaming 失败: {e}")
+
+        # 创建后台任务，不阻塞当前流
+        asyncio.create_task(_do_update())